The goals of this career development award are to expand the candidate's fundamental knowledge in clinical research through a formal course work program, help integrate the candidate into the academic research community, and to provide the experience and knowledge she will need to successfully develop future independent clinical investigations. This study's purpose is to evaluate early factors involved in the etiopathogenesis of idiopathic osteoarthritis (OA). Abnormal dynamic joint loading, muscle weakness, and proprioception deficits have been independently studied and linked to OA. The literature suggests that these factors may be interrelated; however, no single study has looked at these factors together in the pathogenesis of OA. The study population is chosen based upon the candidate's recent investigational findings: that subjects with advanced unilateral hip OA more commonly develop OA of the contralateral knee rather than the ipsilateral knee and that these subjects have higher dynamic joint loads at the contralateral knee relative to the ipsilateral knee before and after hip replacement. This is a cross-sectional evaluation of the knees of 45 subjects with symptomatic early unilateral hip OA and 45 subjects with endstage unilateral hip OA. The specific aims are to investigate relationships between loading, muscle strength, and proprioception of the knees, to identify asymmetries in these factors between the ipsilateral and contralateral knees, and to evaluate these factors in both early and endstages of unilateral hip OA. Subjects will undergo interview, physical exam, and radiography. Specialized testing will include dual x-ray absorptiometry, gait analysis, proprioception evaluation and muscle strength testing of both knees. The data will be evaluated to assess specific associations between the factors, to assess asymmetries in the factors between the subjects' knees, and to demonstrate whether similar asymmetries are present in both early and endstages of unilateral hip OA. The results from this investigation can significantly impact our understanding of neuromechanical mechanisms in the pathogenesis of OA and may provide new avenues for therapeutic and perhaps primary prevention intervention in OA.